Traditional ink-jet systems involve jetting a solution of ink onto a receiver according to a desired positive image. For example, where the desired image requires light absorbance of a particular wavelength at a particular point, an ink having a dye capable of absorbing at that wavelength is typically applied to a receiver at a corresponding point to effect the desired absorbance. Accordingly, an image is formed by applying inks having dyes or pigments of known absorbance to a receiver to form an image with a desired spectral ‘footprint’ corresponding to the spectral properties of the dyes applied at the various points on the receiver. For many applications, this method is effective at accurately representing an image.
A problem with using ink-jet printing, particularly when forming high-density and/or high-resolution images is that in order to achieve a high-density image, sufficient material, e.g. dye or pigment, must be present to absorb sufficient light. The absorption depends on the amount of the material and its inherent optical absorption coefficient, as defined by Beer's Law. Many dyes have a high molecular weight and the optical density per gram is not necessarily high. In order to get sufficient density using such dye-based inks, relatively large amounts of dye must be applied to the receiver. In ink-jet printing, images are formed by jetting dyes in inks. However, there is a limit to the concentration of a dye that can be included in an ink to be jetted, because the dye must pass through small ink-jet nozzles and therefore must be a stable solution or a fine suspension of particles suitable for jetting. So in many cases, such as in the forming of masks for use in printed circuit board manufacture, it is not possible to use ink-jet printing to form the mask in a single application. This problem can be overcome by laying down more than one layer of ink, but this increases the time required to form the desired image. Alternatively, the hole-size in the ink-jet head can be increased in order to increase the amount of ink that can be delivered at one time or to increase the concentration of dye that may be included in an ink, but this leads to a disadvantageous loss in resolution.
Problem to be Solved by the Invention
It is desirable to provide a method by which high-density images can be formed by using a simple jetting technique, which is quick and effective. It is further, desirable that such a technique be capable of providing high-resolution images.
Furthermore, it is desirable that printed circuit board masks may be formed by a simple, fast and efficient ink-jet printing method capable of forming high-density high-resolution images, for use in the manufacture of printed circuit boards.
It is still further desirable to provide a simple, fast, efficient and reliable method of generating hard copy medical or X-ray images from digitally stored images.